Degassing and deoxygenating agent for use in casting an aluminium alloy



United States Patent 3,194,695 DEGASSING AND DEOXYGENATING AGENT FOR USE IN CASTING AN ALUMINIUM ALLOY Riirizo Yanagawa, 88 Hagoromo-cho l-chome, Tokyo, Japan No Drawing. Filed May 12, 1961, Ser. No. 109,517 Claims priority, application Japan, May 24, 1960, 35/25,093 2 Claims. (Cl. 148-26) The present invention relates to a degassing and deolriygenating agent for use in casting an aluminium a oy.

The advantages of an aluminium alloy are, for example, low specific gravity, low melting point, and that the casting properties are good. If however, during casting, molten aluminium alloy contacts with water, such as with moisture in the atmosphere, moisture on the surface of the alloy, moisture in the equipment, water produced by combustion and moisture contained in the flux, the molten aluminium alloy decomposes the water to produce hydrogen and oxygen. The nascent hydrogen thus produced is absorbed into said molten metal and the nascent oxygen reacts with the aluminium to form an aluminium oxide. The amount of hydrogen absorbed depends upon the elements constituting the alloy, that is, for example, when magnesium is contained, the amount of hydrogen increases, and when silicon or copper is contained, the amount of it decreases. Such hydrogen and aluminium oxide contained in the molten metal give rise to mold cavities in the cast metal, and thereby deteriorate the mechanical properties of the product.

The primary object of the present invention is to remove during the operation of casting an aluminium alloy, the hydrogen gas absorbed in the molten metal.

In order to remove such absorbed hydrogen gas, a method of, for example, blowing chlorine gas into the molten metal has been conventionally employed. Also, in order to avoid the inconvenience of using the chlorine gas, it has been proposed to use a composition containing chloride, such as zinc chloride or aluminium chloride, as the principal component. Howevenwhen the chlorine gas is employed for removing the hydrogen absorbed in the molten metal, a small part of the molten metal is lost by being converted into aluminium chloride and scattered away, the amount of aluminium loss being 0.15%. Further disadvantages are that the crystalline grains of the alloy become coarse and large, that impurities, such as iron material, caused by corrosion of an iron conduit tube for introducing the chlorine gas, melt into the molten metal, that the mechanical equipment and apparatus are corroded and the health of workers and environment are likely to be injured. Further, when the chlorides are employed, a high temperature in excess of 680 C. is required while on the other hand the lowest possible temperature is preferable since the higher the temperature, the more the hydrogen is absorbed in the molten metal. In the case of a chloride other than aluminium chloride, for example, of Zinc chloride, Zinc or other metal melts into the molten metal and the amount of impurities increases.

Another object of the present invention therefore, is to provide a degassing and deoxygenating agent for use in casting an aluminium alloy, which does not corrode the mechanical equipment and apparatus, is not injurious to the health and can be used effectively at a temperature less than 680 C.

Now, the present inventor has found that the following two compositions are extremely effective in accomplishing the object of the present invention.

The first type of the compositions:

Percent by weight The surface of the molten metal is covered with an oxide film, which simultaneously prevents the molten metal from absorbing gases contained in the atmosphere and from diffusing gasses contained in the molten metal. The oxide contained in the molten metal has the size of approx. 0.01 mm. in diameter and appears to be suspended in the molten metal. It is considered that the oxide becomes a nucleus which converts atomic hydrogen into molecular hydrogen and separates the molecular hydrogen from the molten metal, and results in difiusing the hydrogen. Therefore, the hydrogen contained in the molten metal will be readily eliminated by removing the oxide existing on the surface of and in the molten metal, which thereby becomes clear and pure. v

The degassing and deoxygenating agent of the present invention has such functions as to remove the hydrogen from the molten metal and to prevent the structure of the molten metal from becoming coarse and large by removing the oxide therefrom. The degassing and dcoxygenating agents of the present invention are applicable to all aluminium alloys other than an aluminium-magnesium alloy. The present degassing and dexoygenating agent may be employed at temperatures including the range of 620 C. to 750 C. and in the amount of 0.2 to 1.0% by weight of the aluminium alloy to be degassed and deoxygenated.

The method of using the degassing and deoxygenating agent of the present invention is as follows:

The moment the ground metal is molten at about 600 C., or when the molten metal is in an amorphous state containing some lumps, the present degassing and deoxygenating agent is scattered over the surface of the molten metal in the proportion of 0.2 to 1.0%, -i.e., at an amount of 200 to 300 g. per Kg. of the molten metal. Then, while the temperature is being controlled, the molten metal is stirred up and down for two or three minutes so that the degassing and deoxygenating agent scattered on the surface may sink into the molten metal. The molten metal is then heated to a casting temperature, and, after removing a slug which has floated up on the surface, is cast into a mold.

The degassing and deoxygenating agent of the present invention scattered on the surface of the molten metal is purple in color and changes to pink as treatment progresses. The present degassing and deoxygenating agent is smokeless and odorless while in use and its reaction ends in a short time.

The present degassing and deoxygenating agent is brought into contact with the molten metal by stirring, and, after absorbing the hydrogen gas and the oxide in the molten metal, it floats up on the surface of the molten metal as a slug which is in the form of dry powder and can be easily removed from the surface of molten metal.

3 Thus, the present degassing and deoxygenating agent effects purification of metal.

The metal cast by using the present degassing and deoxygenating agent has good mechanical properties as shown in the following table of test results:

Test sample: Aluminium alloy die casting No. 12- ADC 12.

Chemical components (percent) Cu 1.81 .2 Si 105-12 Mg 0 3 Zn 1 0 Fe 1.3 Mn 0.5 Ni 0.5 Sn 0.3 Al Balance [Molten metal-70 kg.; added agent, 0.3%210 g.]

Test results Test condition-casting temp., C. Tensile Elonga- Durability strength tion, kgJmmfl kgJmm 2 percent Average 21. 7 2. 0 12.8

4 I claim: 1. A degassing and deoxygenating agent consisting essentially of the following composition:

Percent by weight Lithium chloride, LiCl 2-10 Sodium fluoride, NaF 5-40 Fluorite, CaF 5-20 Cryolite, Na AlF 2-20 Common salt, NaCl 5-40 Potassium chloride, KCl 5-30 whereby the proportions of the compounds of the said agent selected total about 2. A degassing and deoxygenating agent consisting essentially of the following composition:

Percent by weight 'Hexachloroethane, C Cl 3-40 Lithium chloride, LiCl 2-20 Ammonium zinc chloride, ZnCl -3NH Cl 3-20 Potassium silicon fluoride, K SiF 3-20 Borax, Na B O- -10H O 2-10 Soda ash, Na CO 1-5 Silica sand, SiO l-5 whereby the proportions of the compounds of the said agent selected total about 100%.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Griffin et al., Investigations With Aluminum Alloy Castings, Metal Industry, Aug. 15, 1947 (pp. 152).

DAVID L. RECK, Primary Examiner.

RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners. 

1. A DEGASSING AND DEOXYGENATING AGENT CONSISTING ESSENTIALLY OF THE FOLLOWING COMPOSITION:
 2. A DEGASSING AND DEOXYGENATING AGENT CONSISTING ESSENTIALLY OF THE FOLLOWING COMPOSITION: 